1. Field of the Invention
The invention relates to a control apparatus for ac-powered lamp units, more particularly to a control apparatus that permits operation of an ac-powered lamp unit as an emergency lighting device.
2. Description of the Related Art
The conventional lighting arrangements found in corridors and stairways of buildings are designed to operate only when commercial ac power is available. Thus, emergency lighting devices must be installed to provide light in the event of a power outage. The conventional emergency lighting device generally includes at least one lamp unit and a storage battery. The lamp unit is disabled when commercial ac power is available. At the same time, the commercial ac power is converted into dc power for charging the storage battery. In the event of a power outage, the storage battery is connected automatically to the lamp unit, thereby enabling the latter to generate a light output.
Because power outages seldom occur nowadays, the conventional emergency lighting device functions primarily as a back-up lighting device. As such, the conventional emergency lighting device is not used efficiently, and operability of the conventional emergency lighting device cannot be detected unless periodic maintenance is performed. Moreover, because the conventional emergency lighting device is in a back-up state most of the time, unnecessary charging of the storage battery is performed for prolonged periods of time. The service life of the storage battery is adversely affected, thereby necessitating periodic inspection of the storage battery for replacement of the latter in the event of damage.